This invention relates broadly to automatic quality control inspection of manufactured products, and relates more particularly to an automatic electro-optical system for inspecting graphic indicia on a product to determine whether the product is the same as a previously inspected prototype.
The invention is useful, for example, for the purpose of inspecting assembled computer keyboards to determine whether every one of over ninety key positions contains a key having the correct graphics thereon, having the correct orientation and having the correct colors and contrasts. Quality control inspection of computer keyboards by humans is difficult and inaccurate because of the visual complexity of the keyboards produced, and because of the profusion of keyboards for special-purpose computer applications involving keys with a great variety of graphics thereon. Accordingly, there has been a need for a vision system capable of performing the inspection of keyboards without making errors such as the fatigue-induced errors made by human inspectors. However, previously known automatic inspection systems have not been successful in inspecting products such as keyboards because the graphics to be recognized on each key may occupy a very small proportion of the surface of the key, and the many keys are somewhat spaced apart in a keyboard area which is too large to be scanned by a video camera. That is, it has not been practical to scan the large keyboard area with a sufficiently great resolution to locate and recognize very small distinguishing graphic elements on individual keys, since the essential graphic information occupies a very small proportion of the keyboard area and occupies uncertain locations in the keyboard area.
A paper entitled "Automatic Optical Inspection of Keyboards" by Joseph Wilder appeared in the Record of the Workshop on Industrial Applications of Machine Vision, May, 1982, and is incorporated herein by reference.